Antibiotic elution profile and physical properties of a novel calcium phosphate cement material

Calcium phosphate cement (CPC) is an injectable, self-setting artificial bone material that has recently been used as a drug delivery system for bone infection therapy because of its high capacity for antibiotic elution. Despite this advantageous property, the mechanical strength of CPC dramatically decreases upon impregnation with certain types of antibiotics. A novel CPC material (CPC-A) with four-fold higher initial compression strength than that of conventional CPC (CPC-B) was developed by decreasing the median particle size of alpha-tricalcium phosphate powder in CPC from 6.34 to 2.30 mu m. However, the elution profile and mechanical strength of the material following antibiotic impregnation remain unclear. In the present study, we compared the elution profiles and physical properties of CPC-A and CPC-B impregnated with vancomycin hydrochloride (VCM) and gentamicin sulfate (GM). CPC-A showed 3.6-fold higher initial (1 h after hardening) compression strength than CPC-B, even when impregnated with VCM. Scanning electron microscopy and porosimetry analyses revealed that the high compression strength of CPC-A was attributable to the densely arranged micro-porous structure. The small pores, which had a median size of 11.3nm and served as passages for antibiotic elution, reduced the VCM elution rate and promoted long-term (18-week) antibiotic release compared to CPC-B, which contained larger pores (19.6 nm) and did not release VCM beyond 16 weeks. In contrast to VCM, GM impregnation did not markedly affect the compression strength of either material, and the GM elution profiles from CPC-A and CPC-B were nearly identical throughout the measurement period. Taken together, these findings demonstrate that the novel CPC material CPC-A has higher initial compression strength than conventional CPC and the potential for prolonged antibiotic release, suggesting that CPC-A would be an effective bone substitute material, particularly for bone infection therapy. (C) 2016 The Ceramic Society of Japan. All rights reserved.